There is a technique of detecting locations and directions of other vehicles by using images photographed by a camera mounted on a vehicle. The technique detects headlights and tail lamps of the other vehicles at night to generate information of the other vehicles on the basis of the detected information. It is preferable to set the headlights to high beams during traveling at night if there is not a vehicle in front in order to better the visibility of a driver, and to set the headlights to low beams according to the vehicular distance if there is in front. Therefore, it is essential for the technique to detect the distance from the own vehicle to a preceding vehicle in front or an opposing vehicle. As a method of calculating a vehicular distance, the camera mounted on the vehicle photographs the front state of the vehicle, and analysis of photographed images is performed to thereby calculate the vehicular distance. Since it has a limited dynamic range, a CCD or CMOS camera has the difficulty in uniformly photographing an object having such a large difference of intensity as that between the headlights and the tail lamps. In addition, since the incident quantity of light into the camera is dependent on a distance from a light spot, if the headlights are near and the tail lamps are far, the apparent difference of intensity will further expand. Human eyes usually dazzle, even if they are about 200 m far from the high beams. Therefore, the light distribution control is required to detect even a vehicle of some hundred meters distant. To adjust the exposure to the intensity of the far tail lamps will cause a blooming with strong possibility, because the quantity of light from the near headlights is too abundant. And, to adjust the exposure to the intensity of the near headlights will make the far tail lamps dim, which makes the calculation of distance difficult.
In order to solve this problem, there is a well-known technique, which prepares an imaging device having a lens with a blue filter mounted on and an imaging device having a lens with a red filter mounted on. The blue filter detects the headlights of an opposing vehicle, and the red filter detects the tail lamps of a preceding vehicle. For example, the method of the Patent document 1 saves a mechanical scanning device, and realizes an inexpensive system with a simplified construction. However, it employs two imaging devices and two lenses, and imposes double the cost on the optical system. Since each of these two recognizes the headlights and the tail lamps separately, it is possible to absorb the difference of intensity due to the difference of the headlights and the tail lamps, but it is difficult to absorb the difference of intensity due to the difference of distance. Accordingly, if there is a vehicle near and a vehicle far at the same time, the blooming and so forth will lower the detection accuracy of the locations of the vehicles.
Further, the mixture of noise light spots such as a traffic light, streetlight, and vending machine into the light spots of vehicles becomes a subject of discussion on the detection of the headlights and tail lamps. The detection of vehicles is essential to the application software of the light distribution control, ACC, and pre-crush safety and so forth. The light spots other than those of the vehicles have to be excluded as the noises. However, if the above noise light spots are mixed, they will be falsely recognized as the light spots of the vehicles, which will give a serious influence to the behavior of the application software. In order to eliminate the influence of these noise light spots, the Patent document 1 proposes the method of excluding the light spot of a streetlight. This method utilizes the characteristics of the light spot of a streetlight to thereby differentiate the headlights and the tail lamps. That is, the Patent document 1 describes that the exclusion is possible through utilizing the fact that the light spot shifts to the upper part of the screen as the vehicle continues to travel, or by utilizing the flicker inherent to the fluorescent lamps.
[Patent document 1] JP-A No. 519744/2001